(1) Field of the Invention
The present invention relates to an apparatus for adjusting characteristic parameters for a color CRT (abbreviation for Cathode Ray Tube) television receiver. Parameters including convergence, distortion of lines (also called bars) over time in a CRT, and image distortion at each line location.
The present invention relates, particularly, to an apparatus for measuring a convergence state of a color CRT television receiver and/or for measuring relative distortion (image distortion) at each line location in the color CRT and also distortion of the lines due to aging (deterioration with time) of the CRT.
(2) Description of the Background Art
Various types of convergence measuring apparatus of the phase detection type have been proposed which measure a convergence state of a color CRT television receiver.
One of the previously proposed convergence measuring apparatus described above is exemplified by Japanese Patent Application No. (Showa) 63-310670 filed on Dec. 8, 1988.
The previously proposed color CRT television receiver measuring apparatus includes a pattern generator, a photo sensor, and a calculator.
The pattern generator outputs a video signal to the color CRT for measurement. The pattern generator gradually shifts lines in the vertical or horizontal direction on an area of a tube face of the color CRT and generates a video signal which displays a white pattern on another area thereof.
The photo sensor, disposed opposing the tube face, has a directive sensitivity capability with uni-modal characteristic for detecting the light intensity values of each primary color from the CRT screen. Data detected by the photo sensor is output to the calculating means (calculator). The calculating means calculates a misconvergence quantity from the light intensity data of each primary color derived on the basis of the output of the photo sensor.
The photo sensor is disposed on an arbitrary position of the tube face of the color CRT. The pattern generator displays the lines for the respective primary colors on the tube face of the color CRT. The calculating means prepares an envelope curve for each primary color on the basis of the output of the photo sensor to derive the position of the peak value of each envelope curve and calculates a misconvergence quantity by comparing the positions of the peak values for each respective primary color.
The measurements of such misconvergence quantities as described above are carried out at a plurality of positions on the tube face of the color CRT by manually changing the position of the photo sensor on the tube face.
FIG. 2 shows the structure of a photo sensor as described above.
Referring to FIG. 2, the above-described photo sensor includes a casing 230 having an opaque main body casing 230a and a transparent glass 230b forming one end of the main body casing 230a.
A light receiving element 231 is disposed within the end of the casing 230, the light receiving element 231 detecting incident light via the transparent glass 230b, a face of the glass 230b being constituted as a contact face 232. Thus, the light receiving element 231 detects light emitted from the tube face 202 when the photo sensor is disposed so as to bring the contact face 232 thereof into tight contact with the tube face 202 of the CRT.
It is noted that it is necessary to measure the image distortion as well as convergence when television receivers are assembled.
Cathode Ray Tubes (CRT) display an image when fluorescent irradiating points emit light from the CRT tube face after being charged by an electron beam. Therefore, an appropriate image cannot be achieved when the direction of the electron beam is deviated from a desired position due to aging or other causes of deviation from the desired position. Hence, to correct such problems, lines in the vertical and/or horizontal direction are generated on the tube face of the CRT to measure distortion of lines over time (time distortion, or time lapse distortion) in the CRT and relative distortion (image distortion) at respective positions on the CRT tube face and to adjust the positions of lines on the basis of the measurement results so that no distortion occurs.
It is noted that for line distortion measurements, the positions of lines are measured with a scale arranged on the tube face or with a QC (Quality Control) scope.
The previously proposed convergence measuring apparatus has the following drawbacks.
Since the dimensions and thicknesses of tube faces are different in various makes and models of color CRTs, intervals between lines and the distance (refer to l in FIG. 5) between the irradiating points on the tube face and the photo sensor are different according to the make and/or model of the color CRT.
Therefore, since the directive sensitivity capability of the photo sensor has a constant unimodal characteristic, the difference between the detected maximum value and the detected minimum value of light intensity data becomes inaccurate in a case when the line interval with respect to the distance between the fluorescent screen and photo sensor is not held to a predetermined constant. An envelope curve derived by interpolation of the detected output of the photo sensor will be distorted with respect to a sinusoial waveform. When the envelope curve is distorted, the position of an accurate peak value cannot be calculated and an erroneous misconvergence quantity will be derived.
A white area is provided on the tube face (screen) of the CRT so as to suppress voltage variations in the area of the CRT 1 which is displaying color(s), to allow more accurate measurement of color characteristics. It is noted that when lines of green (G), red (R), and blue (B) respectively, are displayed solely, the beam current voltage of the color CRT changes. Therefore, a positional change in the color electron peak occurs. Consequently, the white area needs to be provided to prevent voltage fluctuation during measurement of the CRT.
However, since measurements cannot be made on the white area of the tube face, it is necessary to change the location of the white area as different portions of the tube face are being tested. This operation is carried out by, e.g., an operator keying change data for the white area through a keyboard. Consequently, such measurements are time consuming and operation is troublesome.
Additionally, a longer time is also required to measure convergence. For example, the following measurement time is required to calculate a single misconvergence quantity during measurement; suppose that the number of samplings required to prepare the envelope curve of any one of green, red, or blue is S and a unit of time for line shift is t. The light intensity data for each of green, red, and blue is sampled. The measurement time for the misconvergence quantity of either the vertical or horizontal direction is expressed as follows: EQU T (measurement time) =3 (three colors).times.S (the number of samplings).times.t (unit shift time).
In order to improve the measurement accuracy, it is necessary to increase the number of samplings (S).
However, an increase in the number of samplings mans an increase in the measurement time. An irrefutable relationship exists between measurement accuracy and measurement time.
Unit shift time (t), however, cannot be set any faster due to the functional limitations of such a measuring apparatus.
Furthermore, the brightness of lines is often reduced due to video frequency instability early in the measurement due to transient characteristics of the video circuit, the pattern generator and the color CRT, etc.
Therefore, initially, light intensity data is detected at a value lower than its actual value due to error in the detected output of the photo sensor (light intensity data). When error is present in the light intensity data, the position of a peak value derived from the light intensity data will be deviated and measurement accuracy is lowered.
In addition, the photo sensor of the previously proposed measuring apparatus has a number of drawbacks, a detailed explanation thereof will be made with reference to FIG. 2.
When the contact face 232 of the photo sensor is pressed against the tube face 202 of the CRT, the contact face 232 is inclined and contacted with the tube face 202a. If the horizontal axis n of the contact face 232 must be disposd so as to be vertical with respect to the tube face 202 it is troublesome for an operator to bring the contact face 232 into correct alignment with the tube face 232 due to the slightly rounded surface of most CRT screens. Once the contact face 232 is in tight contact with the tube face 202 of the CRT, the casing 230 may be easily displaced in the arrow-marked directions in FIG. 2 while being handled by an operator. The slight displacement causes variations in the positions of the contact face 232 and the light receiving element 231 such that the photo sensor may erroneously detect the position of the lines described above.
Finally, the previously proposed line distortion measuring apparatus has the following drawback, that is to say, measurement by scale and QC scope cannot measure line distortion with high accuracy since the operator must manually read a graduated scale affixed to the CRT which itself has a certain thickness. This, when coupled with the curved surface of the CRT can lead to misreading due to the operator's viewing angle, the portion of the screen being read, etc.
Since highly accurate CRTs are now demanded, the above-described prove increasingly inadequate. As the burdens of measurement and scale reading are imposed on the operator, it becomes desirable to find a way to measure line distortion in CRT equipment in the simplest, most efficient way possible.